parser: forbid unsafe code

This way, can avoid relying on a sanitizer when fuzzing. For now, we only allow unsafe code in a few specific cases in the lexer.

parser/src/lib.rs

@@ -2,6 +2,7 @@
 //
 // For the full copyright and license information, please view the LICENSE
 // files that was distributed with this source code.
+#![forbid(unsafe_code)]
 
 mod ast;
 mod diagnostics;